1. Field of the Invention
The invention relates to a method of indirectly connecting two parts and somewhat more particularly to such a method whereby two metallic layers are applied under vacuum to the surfaces to be connected and are then brought into contact with one another without ventilation under the maintained vacuum to form the desired bond.
2. Prior Art
German Publication Application (DT-OS) No. 2,253,913 discloses a method of indirectly connecting two parts by applying, under vacuum, metallic layers on the surfaces to be connected and forcing such layers against one another to form a bond. In this method, an acousto-optical building component comprised of, for example, quartz is joined with an electro-mechanical converter, such as a piezo-electric structure so that the resultant structure comprises an acoustical light deflection system. In order to achieve the desired bond between such parts, two consecutive metallic layers are provided on such parts. A first layer is composed of gold and chromium and the other layer is composed of indium. The metals forming such layers are vaporized from suitable sources within a vacuum chamber and are deposited on the surfaces of the respective parts to be connected, which are then bonded to one another via such layers. In this system, the layer composed of gold and chromium has a thickness of a few thousand Angstrom units and the indium layer is of approximately the same thickness. After such metallic layers have been applied to the respective surface to be joined, the free surfaces of the respective indium layers are brought into contact against one another and compressed under vacuum for a few minutes at a pressure of about 2,800 to 3,500 N/cm.sup.2 (Newtons per square centimeter) so that such indium layers and the parts supporting such layers become interconnected by cold welding.
However, if parts consisting of a pressure-sensitive material are to be so-joined with one another or with some other part, a substantial danger exists that destruction or damage to such parts might occur at the relatively high pressures required to accomplish such cold welding or bonding. Such a danger exists, for example, in attempting to cold weld an acousto-optical building component consisting of lead molybdate or an electro-mechanical converter composed of lithium niobate.
Another method of producing acoustical light deflector systems is suggested by French Pat. No. 2,162,743 wherein an acousto-optical component composed of, for example, lead molybdate is directly connected with an electro-acoustical transducer composed of, for example, lithium niobate. In this system, a plurality of metallic layers, comprised of a titanium layer having a thickness of about 200 Angstroms, a titanium-gold layer having a thickness of about 200 Angstroms, a gold layer having a thickness of about 3,000 Angstroms are consecutively provided, as by vaporization on one another, on the surfaces to be joined in a vacuum chamber. Subsequently, such metallic layers having a combined thickness of about 6,400 Angstroms are welded or bonded together under vacuum whereby a temperature of about 60.degree. C. (140.degree. F.) and a pressure in the order of magnitude of about 2,000 N/cm.sup.2 must be withstood. This pressure is below that suggested by the above DT-OS '913 for cold welding because by utilizing temperatures in the vicinity of 60.degree. C., a kind of thermo-compression welding occurs. However, an elevation of the welding temperature with only a slight reduction in pressure still presents a danger of damaging or destroying the parts to be joined. Further, stress fissures or the like may occur with such thermo-compression welding since the parts to be joined may have a different coefficients of heat expansion.